The invention relates to an internal combustion engine for a motor vehicle including an exhaust gas turbocharger with two exhaust gas lines leading from the engine and a flow control device for interconnecting the exhaust gas lines and/or for bypassing the turbine and to a method for controlling such an internal combustion engine.
Due to the continuous tightening of engine emission limit values, for example the NOx and soot emission values of diesel engines, the requirements of internal combustion engines with exhaust gas turbocharger are also tightened. Thus, increasing requirements with regard to the charge pressure provision for example with regard to the charge pressure provision over average or high load operating ranges of the internal combustion engine are becoming tighter, whereby exhaust gas turbochargers have to be scaled down geometrically. In other words, the required high turbine performances of exhaust gas turbochargers are realized by an increase of the build-up capacity or the reduction of the operating flow capacity of the exhaust gas turbochargers in cooperation with the respective internal combustion engine. A further negative influence with regard to the performance of exhaust gas turbochargers results from exhaust gas treatment systems arranged in the exhaust gas tract downstream of the exhaust gas turbine of the exhaust gas turbocharger, for example soot filters, catalytic convertors or SCR plants. These exhaust gas treatment systems lead to a pressure increase at an outlet of the exhaust gas turbocharger which reduces the pressure drop across the turbine describing the performance of the exhaust gas turbocharger. The turbine pressure drop can be determined as the quotient of a pressure in front of the turbine wheel or before the entrance to an exhaust gas guide section and a pressure behind, or at the exit of, the exhaust gas guide section. The turbine size has again to be designed for smaller values hereby, in order to be able to satisfy the performance requirement of the compressor side. As a result, a sufficient exhaust gas amount is not available even with an exhaust gas turbocharger, whose exhaust gas guide section has two spiral channels through which exhaust gases flow independently, for achieving the required charge air pressure on the compressor side. Due to the reduced geometrical dimensions of the spiral channels, comparatively high flow losses are generated because of wall frictions, which leads to a further decrease of the degree of efficiency. The same is true for exhaust gas turbochargers, which have guide vane elements in the exhaust gas guide passages upstream of the turbine wheel and downstream of the spiral channels. These guide vane elements thereby permit a pressure increase in front of the turbine wheel of the exhaust gas turbocharger, so that an improved degree of efficiency of the exhaust gas turbocharger can be achieved even with a low mass flow of exhaust gas in the first spiral channel.
Even though exhaust gas turbochargers having an exhaust gas guide section with two spiral channels and corresponding guide vane elements are comparatively cost-efficient in their production, elaborate and cost-intensive measures are necessary to make an improvement of their degree of efficiency and corresponding reductions in fuel consumption of the internal combustion engine possible. A further problem with regard an exhaust gas recirculation capability of these exhaust gas turbochargers arises in connection with the required combustion air supply in particular in the lower or medium speed range of the internal combustion engine. With the usual design constraints, which are provided at the nominal operating point of the internal combustion engine based on gas change considerations and fuel consumption considerations, only a limited operating range can be handled in an optimum manner, even with a double path exhaust gas inlet guide arrangement.
It is the object of the present invention to provide an internal combustion engine with an exhaust gas turbocharger and a method of controlling such an internal combustion engine, such that an improvement of the degree of efficiency in a relatively large operating range of the exhaust gas turbocharger is obtained.